1. Field of the Invention
The present invention broadly relates to computer systems, and more particularly, to a stiffener for a printed circuit board that is to be mounted on a chassis inside a computer system housing.
2. Description of the Related Art
Modem computer systems generally include a housing or enclosure, a display device and an external command/data input device. The display device may be a CRT (cathode ray tube) monitor, e.g., in a desktop computer system, or it could be a TFT (thin film transistor) screen, e.g., in a portable laptop computer. The external input device may be a keyboard, a pointing device, e.g., a mouse, or a combination of them. The system housing is an enclosure that houses the hardware components that perform, along with necessary software, various processing tasks as requested by the user. The housing may also include one or more power supplies to supply proper electrical power to various electronic hardware circuit elements. Auxiliary storage device drives, e.g., a floppy disk drive or a CD-ROM drive may also be housed within the computer system housing. Additionally, hard disk drive for large amount of data storage is almost invariably included within the computer housing for greater digital information storage capacity.
Generally, a computer system housing includes a metal chassis upon which one or more computer system components, e.g., cooling fans, printed circuit boards, hard disk drive, etc., are mounted during system fabrication. The metal chassis may then be covered with one or more panels to enclose the system components.
A printed circuit board may generally contain a number of electronic devices, such as, resistors, capacitors, power supply unit, memory chips or memory cards, one or more microprocessors, one or more co-processors, various integrated circuits, etc. A printed circuit board may also contain connectors for one or more of these devices and additional attachment units. One or more of these connectors may require unusually tight tolerances on the flatness of the printed circuit board in the vicinity of the connector to allow for stability in electrical connections and also to maintain a tighter grip on an electronic component mounted on the printed circuit board through the corresponding connector.
A printed circuit board is generally mounted directly on the computer system chassis with requisite electronic components already on the printed circuit board. However, any future insertion onto a directly chassis-mounted printed circuit board of a component or electronic part by a user or at a later stage during fabrication of the computer system prior to shipping may result in developments of small cracks or breakage points along the conducting paths of the printed circuit board. Additionally, a heavily loaded printed circuit board that is directly mounted on the system chassis may similarly get damaged during mounting or during later upgrading. Furthermore, electronic components inserted into connectors requiring substantially flat circuit board surface near the connecting area may not obtain requisite tightness of electrical connections on a loaded printed circuit board.
It may therefore be desirable to provide a back plane support for a printed circuit board prior to its being mounted on the metal chassis of the computer system housing.
The problems outlined above may in large part be solved by a computer system housing where a stiffener is placed on a wall of the metal chassis within the housing and between a printed circuit board and the wall so as to provide a back plane support for the printed circuit board. The printed circuit board may be attached to the stiffener prior to mounting the complete assembly onto the chassis. Alternately, the stiffener may first be mounted on the chassis, and the circuit board carrying required electronic components may then be mounted on the stiffener.
The stiffener may include a support frame made up of a plurality of longitudinal bars. The longitudinal bars may be manufactured pre-attached using a single progressive tool during the support frame fabrication, or may be individually manufactured and later attached in the desired shape to form the support frame structure. Each longitudinal bar may have one or more holes that may correspond to similar holes in the circuit board to be mounted. The holes receive fasteners to securely fasten the circuit board to the stiffener. In an alternative embodiment, each longitudinal bar may have a fixed number of holes irrespective of the corresponding number of holes in the circuit board to be fastened. A horizontal strut may also be manufactured as part of the support frame structure or as an independently attachable unit. The horizontal strut may provide additional back plane support to the printed circuit board carried by the support frame.
Further, the stiffener may include one or more vertical struts that may be attached to the support frame for additional support to those portions of the circuit board that may be prone to carry dense circuitry or that may require tighter circuit board tolerances around one or more connectors present therein. In one embodiment, each longitudinal bar, one or more vertical struts and the horizontal strut may have one or both edges raised to a predetermined height to form a spacing between the circuit board and the stiffener. This additional spacing may be desirable to prevent direct contact of circuit board""s conducting paths with the stiffener frame.
The back plane support provided by the stiffener may reduce damage to the printed circuit board due to pressures exerted during component mounting on the circuit board that is already installed on the chassis. Additionally, a circuit board carrying densely populated electronic components may be easily mounted on or removed from the chassis without damage. Requisite flatness of the printed circuit board may also be maintained in the vicinity of larger connectors with the help of vertical struts.